Corticobasalganglionic Degeneration

05 November 2004

What is corticobasal degeneration?
Corticobasal degeneration (CBD) is a rare neurological disease in which parts of the brain deteriorate or degenerate. CBD is also known as corticobasal ganglionic degeneration, or CBGD.

Several regions of the brain degenerate in CBD. The cortex, or outer layer of the brain, is severely affected, especially the fronto-parietal regions, located near the center-top of the head. Other, deeper brain regions are also affected, including parts of the basal ganglia, hence the name "corticobasal" degeneration. The combined loss of brain tissue in all these areas causes the symptoms and findings seen in people with CBD.

What causes the degeneration of brain tissue in CBD?
Unfortunately, the cause of CBD is entirely unknown. There is currently no strong evidence to suggest CBD is an inherited disease, and no other risk factors, such as toxins or infections, have been identified.

Studies of brain tissue of individuals with CBD show certain characteristic cell changes. Similar, although not identical, changes are observed in two other neurodegenerative diseases, Pick's disease and progressive supranuclear palsy. These changes, involving a brain protein called tau, have provided researchers some initial clues in their search for the causes of CBD.

What are the symptoms of CBD?
Symptoms of CBD usually begin after age 60. The initial symptoms of CBD are often stiffness, shakiness, jerkiness, slowness, and clumsiness, in either the upper or lower extremities. Other initial symptoms may include dysphasia (difficulty with speech generation), dysarthria (difficulty with articulation), difficulty controlling the muscles of the face and mouth, or walking and balance difficulties. Symptoms usually begin on one side of the body, and spread gradually to the other. Some patients (probably more than commonly recognized in the past) may have memory or behavioral problems as the earliest or presenting symptoms.

CBD is a progressive disease, meaning the symptoms worsen over time. Over the course of one to several years, most people with CBD gradually worsen, with symptoms progressing to involve upper and lower extremities and other body regions. Symptoms of advanced CBD include:

• parkinsonism (rigidity, slow movements, postural instability)
• tremor
• myoclonus (sudden, brief jerky movements)
• dystonia, including blepharospasm
• speech difficulty
• mild-to-moderate cognitive impairment (memory loss, difficulty planning or executing unrehearsed movements, dementia)
• sensory loss
• "alien hand/limb" phenomenon (difficulty controlling the movements of a limb, which seems to undertake movements on its own, sometimes combined with a feeling that the limb is not one's own)

How is CBD diagnosed?
Early in the disease course, it is often difficult to distinguish CBD from similar neurodegenerative diseases. Diagnosis of CBD involves a careful neurological exam, combined with one or more types of laboratory evaluations. Electrophysiological studies, including an EEG (electroencephalogram), may show changes in brain function over time that are consistent with the neurodegeneration. CT or MRI scans can also be used in this way, providing images of asymmetric atrophy of the fronto-parietal regions of the brain's cortex, the regions most frequently involved in the disease.

How is CBD treated?
Unfortunately, there are no drugs or other therapies that can slow the progress of the disease, and very few that offer symptomatic relief. Tremor and myoclonus may be controlled somewhat with drugs such as clonazepam. Baclofen may help reduce rigidity somewhat. Levodopa and other dopaminergic drugs used in Parkinson's disease are rarely beneficial, but may help some CBD patients.

Physical therapy exercises may be useful to maintain range of motion of stiff joints. This may prevent pain and contracture (muscle shortening), and help maintain mobility. Occupational therapy may be used to design adaptive equipment that supports the activities of daily living, thus helping to maintain more functional independence. Speech therapy is used to improve articulation and volume.

What is the usual course of CBD?
A person with CBD will usually become immobile due to rigidity within five years of symptom onset, and may require a gastrostomy tube for feeding at some point before that. Most often, within ten years of onset, pneumonia or other bacterial infections may lead to life-threatening complications.